Testing of phosphor bronzes

ABSTRACT

The invention is predicated on the discovery that phosphor bronze strip may or may not have a thin coating of an oxide thereon which is formed during annealing of the strip. Coating, when present, substantially reduces die life when precision stamped and formed parts are being made from the strip. Coating is not detectable by previously known quality controls. Method is disclosed for determination of the presence or absence of the coating and, therefore, the suitability of a given lot of phosphor bronze strip for the manufacture of stamped and formed parts.

United States Patent 1 Brandeau et al.

1| 3,710,620 51 Jan. 16, 1973 [54 TESTING OF PHOSPHOR BRONZES [75] .lnventors: Edward-Peter Brandeau; Quentin Roosevelt Chafiee;. Robert Lewis Gitt, all of Winston-Salem, N.C.

[73] Assignee: AMP Incorporated, Harrisburg, Pa. 22 Filed: ne 21,1970

[21]- Appl. No.: 99,814

[52] US. Cl. "73/159, 73/150, 73/432 [51] Int. Cl. ..G0ln 33/20 [58] Field of Search ..73/7, 87, 104, 150, 432 R, 73/101, 159

[56] References Cited I i UNITED STATES PATENTS 1,457,800 6/1923 'Spindel 73/7 Primary Examiner-S. Clement Swisher Att0rneyWilliam J. Keating, Ronald D. Grefe, Gerald K. Kita, Frederick W. Seitchik 57' ABSTRACT The invention is predicated on the discoi/ery that phosphor bronze strip may or may not have a thin coating of an oxide thereon which is formed during annealing of the strip. Coating, when present, substantially reduces die life when precision stamped and formed parts are being made from the strip.'Coating is not detectable by previously known quality controls. Method is disclosed for determination of the presence or absence of the coating and, therefore, the suitability of a given lot of phosphor bronze strip for the manufacture of stamped and formed parts.

3 Claims, 5 Drawing Figures Raring and Jay L PATENTEDJAN 16 I975 SHEET 1 [1F 2 PAIENIEDJAH 16 I973 SHEET 2 BF 2 .Qmm k w m w m N 00- E w AV 6 O 6 6 O 6 9 Au 0 e 5 Au 0 MW 4 Au 0 AU 3 Av \7 o It 2 .9 m Aw m AU 2 o mm-.wn n u .2 627.9435: woz .m wmm O INITIAL 0 FINAL .2 m m w m w m w 09 w a O O 9 A O 5 L c 8 3) O /.f\ 8 A0 A O 0 an 1 mm o if 6 O A 0 an 5 An AG m A0 A0 0 3 Au 0 I 2 w Aw 2 .9 00 h w o v n N .0- AwEIQJdSC wozafiwamm PERCENTAGE TESTING OF PHOSPHOR BRONZES BACKGROUND OF THE INVENTION suitable punches and diesby means of which the strip is blanked and formed into the desired final shape by bending. Stamping and forming methods are used to manufacture a wide variety of articles including-electrical connectors of various types. In some instances, the parts manufactured need not necessarily be precisely dimensioned, that is the dimensional tolerances for the finished parts can be relatively wide, while other parts must be made to extremely close dimensional tolerances. Electrical connecting devices of the general type disclosed in the above-identified Pat. No. 3,320,354 fall into the latter category regarding'the required dimensional tolerances and if the tolerances in the part are not maintained, the electrical performance of the connector will suffer.

The tolerances which are maintained in a succession stock of a given thickness and composition having a given grain size and a given hardness, the die life can be closely predicted by a skilled engineer and the stock used for a given article manufacture is selected with die life in mind as one of the factors to be considered.

We have discovered certain anomalies in die life where precisionparts are being manufactured from phosphor bronze alloys. The term phosphor bronze is generally understood to refer to copper-tin alloys containing 90-98 percent copper with the balance being tin and phosphorus in amounts of 0.1 to 0.25 percent. A so-called grade A phosphor bronze for example may contain 95 percent copper, 4 percent tin, and from 0.01 to 0.] percent phosphorus with minor amounts of lead, iron and possibly zinc present as impurities. A

' phosphor bronze of this composition is useful for a high performance electrical part where a metal having both of articles produced by a stamping and formingdie assembly are dependent upon the initial tolerances built into the punches and dies and on the maintenance of the die during use. A given die may be made to maintain a certain dimension in the finished stamped and formed article to within i0.0002 inch, which is a relatively close tolerance, and when the die assembly is placed in the press, the parts producedshould lie within these tolerance dimensions. As more and more parts are produced from the die, however, the die wears and after a relatively large number of parts have been produced, it will be found that out of tolerance parts will sometimes be produced, the incidence or frequency of these out of tolerance parts increasing as further parts are produced by the dieand wear increases.

In any modern carefully controlled stamping and forming manufacturing operation, it is usually'known precisely how many parts can be produced from a given die before tolerance variations in the parts begin to ap pear and overhaul of the die is required. Such overhaul of the die involves the sharpening of the punches and long been known that die life is dependent upon several good electrical and mechanical properties is required. This alloy is particularly useful in that ithas good spring properties and can be used in electrical contact terminal devices where the spring properties of the metal must exceed those available from the more common brasses- An additional advantage of the phosphor bronzes over the brasses is that they can be used where relatively high temperatures are involved without undue degradation of the electrical connecting device.

In the past, it has generally been accepted in the stampingand forming art that relatively short die life is to be expected where parts are being manufactured from phosphor bronze strip and manufacturers of stamped and formed phosphor bronze part have been resigned to the fact that frequent resharpening or rebuilding of the stamping dies is required if a high degree of dimensional precision is to be maintained in the finished part. Such frequent resharpening or rebuilding of the dies has been required for the grade A phosphor bronze identified above even when the material is relatively soft, that is, where it is one-eighth hard and has been subjected to an annealing operating dies and, under some circumstances, replacement of variableswhich are present in the strip stock being-used in the manufacturing process, such as the chemical composition of the stock, its temper, its history ofheat treatment, and, sometimes, the finish, such as a plating or corrosion product on the surface of the stock. These variables are, therefore, rigidly controlledand in 'a wellordered and carefully controlled manufacturing process, stamped and formed parts are made only from material which has been carefully inspected and'sub jected to the numerous quality controls which are presently available to the stamping and forming art. Thuswhere articles are manufactured from say a brass subsequent to final rolling to its desired thickness.

We have discovered: that the use of phosphor bronze in a stamping and forming operation need not be accompanied by extremely short die life as has heretofore been believed. Particularly, we have discovered that the presence of a extremely thin film, which heretofore has been undetected, on phosphor bronzes shortens die life in the manufacture of stamped and formed parts and that in the absence of this film, protracted die life can be obtained which is comparable to that obtained when the parts are being manufactured from brass or other well-known and easily formed materials. We have further devised methods of determining the suitability of a given lot of phosphor bronze strip for stamping and forming operations and'predicting the die life which can be expected when the parts are manufactured from that lot of material;

It is accordingly an object of the invention to increase the die life of a die being used to manufacture parts from phosphor bronze strip. A further object is to provide a test to determine the suitability of a given lot of phosphor bronze strip for the manufacture of stamped and formed parts. A still further object is to improve the degree'of dimensional precision which can i be obtained in the manufacture of stamped and formed parts from phosphor bronze strip.

These and other objects of the invention are achieved in a preferred embodiment thereof which is briefly described in the foregoing abstract, which is described in detail below, and which is illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of a punch and die used to carry out a test in accordance with the invention.

FIG. 2 is a plan view of the upper surface of the punch of FIG. 1 showing the effect achieved after a test on a non-satisfactory phosphor bronze.

FIG. 3 is a plan view of the lower end of a punch of FIG. 1 showing the effect of an unsatisfactory phosphor bronze.

FIGS. 4 and 5 are plots illustrating the electrical performance of electrical connectors manufactured from an unsatisfactory and a satisfactory phosphor bronze as determined by the instant invention.

The instant invention is predicated on the discovery that phosphor bronze in strip form may or may not have on its surface an extremely thin film of contaminants which adversely affects die life when metal parts are stamped and formed from the strip. As mentioned above, phosphor bronze grade A has been used to manufacture electrical connectors in accordance with the teachings of U.S. Pat. No. 3,320,354. For optimum electrical performance, the dimensional tolerances of connectors of this type must lie within very close ranges and any departure from these extremely tight tolerances results in inferior electrical performance.

During the manufacture of about sixty million terminals in accordance with the above-identified Marley et al. patent, it was observed that some batches of connectors performed extremely well and that when subjected to a standard temperature cycling test and retested for electrical resistance, there was virtually no significant increase in resistance as a result of the temperature cycling. The temperature cycling test was carried out as follows: the samples were placed in a temperature chamber and the temperature was raised to 140 F. This temperature was maintained for 1 hour after which the temperature was lowered, over a period of 6 hours to 40 F. The temperature of the chamber was maintained at 40 F for 1 hour after which it was raised, over a period of 6 hours, to 140 F. The cycle was repeated 512 times and the electrical resistances of the samples were measured at room temperature. The moisture level of the chamber was maintained during the test between the limits of 0.008 to 0.012 pounds of moisture per pound of dry air.

It was also observed that other batches of electrical connectors performed relatively poorly, particularly in that the resistance of the crimped'connection between the connector and the wire increased substantially after the same temperature cycling test was carried out.

In an attempt to determine the cause of these variations in performance, careful records were kept of all stock phosphor bronze used to manufacture connectors and tests were conducted on representative samples of connectors from all batches of materials. Whenever a lot or batch of phosphor bronze was found to produceinferior electrical connectors, samples of this lot were submitted, along with samples of satisfactory strip phosphor bronze, to thorough examinations such as metallographic examinations, examination under electron and scanning electron microscopes, x-ray defraction and x-ray fluorescence examination, and very careful chemical analysis. In all cases, no significant differences were found between lots of phosphor bronze which produced satisfactory connectors and lots of phosphor bronze which produced unsatisfactory connectors. In other words, the available quality control tests, and many tests which were beyond the realm of normally employed quality control tests for material used in the manufacturing process, failed to reveal any cause for variation in the performance of the connectors being manufactured.

In order to determine the suitability of a given lot of phosphor bronze for stamping and forming manufacturing operations, a test procedure was devised as illustrated in FIGS. 1-3. Referring to FIG. 1, a conventional hardened steel stamping punch 2, and a hardened steel stamping die 4 are provided, the punch having a lower end 6 which is adapted to fit within an opening 8 in the upper surface 10 of the die 4. A simple punch and die set of this type is mounted in a conventional punch press and a sample of the stock phosphor bronze 12 is fed through the press to produce stamped or punched openings 14 in the stock. The test is carried out until about 100,000 holes are produced; in other words until the punch and die have been subjected to l00,000

operations on the test specimen l2. Thereafter, the

upper surface of the die 4 and the lower surface of the punch 6 are examined. Where the sample of stock material 12 is unsatisfactory for the manufacture of electrical terminals in accordance with the aboveidentified Marley et al. patent, it will be found that the upper surface of the die 10 will be burnished as indicated at 16in a restricted area immediately surrounding the opening 8. Also, the lower surface of the punch 2 will be burnished as indicated at 18 around the edges of the lower surface. If, on theother hand, the stock material is satisfactory, the appearance of the upper surface of the die 10 and the lower surface of the punch 2 will be uniform and the burnishing effect shown in FIGS. 2 and 3 will not be observed.

It has been determined that if stock material intended for the manufacture of precision parts is tested in accordance with the foregoing procedure and ifthe material passes the test, that is if no burnishing is produced on the punch and die, a relatively long life for the die can be expected before the punches and dies need sharpening or other repairs must be carried out. For example, it is now common practice to obtain in excess of 200,000 parts from a single die before overhaul of the die is required if material which is satisfactory in accordance with the instant test procedure is employed. By contrast, if unsatisfactory material is employed to manufacture the parts, as determined by the instant test, it is usually necessary to overhaul the die afterno more than 20,000 parts have been produced and quite often it is necessary to overhaul the die after only 5,000 parts have been produced.

It has been observed that some samples from some lots of phosphor bronze when subjected to the punch and die test described above will cause burnishing of one of the parts, thatis either the punch or the die, but not the other. As will be explained below, this has now been determined to be the result of the presence of a contaminant on one side only of the stock material but not on the other side.

Referring now to FIGS. 4 and 5, when electrical connectors in accordance with the above-identified Marley patent are manufactured from a material which has been determined to be unsatisfactory in accordance with the instant test, it will be found that the crimped connections produced when the connectors are crimped onto electrical conductors are incapable of with-standing the standard temperature cycling test discussed above.

FIG. 4 shows the resistance in milliohms plotted on a log scale as the abscissa against the cumulative percent age of samples tested on the ordinate. As will be apparent from this test, a substantial increase in the resistance is to be encountered in about 7 percent of the connectors in a given lot produced.

FIG. 5, on the other hand, demonstrates the performance of a lot of connectors produced from satisfactory stock phosphor bronze as tested in ac-- cycling. Connectors exhibiting the statistical behavior of FIG. 4'are, of course, unsatisfactory for most purposes while'those having the behavior of FIG. 5 are satisfactory.

It has been hypothesized that an unsatisfactory lot of phosphor bronze, as determined by the test of the instant invention, has an extremely thin film .of a contaminant on one or both of its surfaces and this contaminant causes extraordinary wear on the dies when parts are stamped from the material. \The available evidence indicates that such in fact is the case and that an extremely thin film of stannic oxide is present on those lots of phosphor bronze which produce the burnishing effect illustrated -in the drawing. The thickness of this film cannot be determined with precision although available evidence indicates that it is less than several hundred Angstrom units thick. As noted previously, this film escaped detection by all of the extremely sensitive tests which are commonly used to determine the quality and the properties of stock material. In other words, none of the presently available routine tests that are used to determine the acceptability of stock material were capable of determining the suitability of stock in accordance-with the instant test.

The available evidence further indicates that the thin film on some lots of phosphor bronze is produced during the annealing operation which follows final rolling and is caused by the presence of available oxygen in the atmosphere of the annealing furnace. If this annealing operation is carried out in a neutral atmosphere or in a reducing atmosphere, no film will be formed. However, a slightly oxidizing atmosphere can result in the formation of the fiim.

It is believed that the burnishing effect illustrated in the drawing is a result of the fact that very slight movement must take place between stock material and a punch and die when a part is stamped from the stock. The presence of an extremely thin film of a very fine abrasive would be expected to burnish the die in the manner shown. It fol ows that other tests involving a highly sensative wear test on the material might be substituted for the test disclosed above.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only.

What is claimed is: v

1. A method of determining the suitability of phosphor bronze strip stock for manufacture of stamped and formed articles within precise dimensional tolerances comprising the steps of:

obtaining a representative sample of said strip stock,

subjecting hardened tool steel testing means under pressure to contact with said sample, and inspecting said hardened tool steel testing means for evidence of burnishing, strip stock which is unsuitable for manufacture of said parts being burnished after said contact with said sample.

2. A method as set forth in claim 1 wherein said step of subjecting hardened tool steel testing means to contact with said sample is carried out by punching holes in said sample with a punch and die.

3. A method of determining the suitability of phosphor bronze strip stock for the manufacture of stamped and formed articles within precise dimensional tolorances comprising the steps of selecting a representative sample of said stock,

feeding said sample intermittently between a punch and die, said punch and the opening in said die having a substantially oval-shaped cross-section, and punching about 100,000 holes in said sample, and

examining the end of said punch and the surface of i said die for burnishing on the end of said punch and on said die in the vicinity of said opening. 

2. A method as set forth in claim 1 wherein said step of subjecting hardened tool steel testing means to contact with said sample is carried out by punching holes in said sample with a punch and die.
 3. A method of determining the suitability of phosphor bronze strip stock for the manufacture of stamped and formed articles within precise dimensional tolorances comprising the steps of selecting a representative sample of said stock, feeding said sample intermittently between a punch aNd die, said punch and the opening in said die having a substantially oval-shaped cross-section, and punching about 100,000 holes in said sample, and examining the end of said punch and the surface of said die for burnishing on the end of said punch and on said die in the vicinity of said opening. 